Secondary, lithium-ion cells and batteries are well known in the art. One such lithium-ion cell comprises essentially a lithium-intercalateable carbonaceous anode, a lithium-intercalateable, chalcogenide cathode, and a non-aqueous, lithium-ion-conducting electrolyte therebetween. The carbon anode comprises any of the various forms of carbon (e.g., coke or graphite fibers) pressed into a porous conductor or bonded to an electrically conductive carrier (e.g. copper foil) by means of a suitable organic binder. A known chalcogenide cathode comprises a crystalline spinel form of manganese oxide bonded to an electrically conductive carrier (e.g., aluminum foil) by a suitable organic binder such as ethylene propylene diene monomer (EPDM).
Lithium-ion cell electrolytes comprise a lithium salt dissolved in a vehicle which may be (1) completely liquid, or (2) an immobilized liquid, (e.g., gelled, or entrapped in a polymer matrix), or (3) a pure polymer. Known polymer matrices for entrapping the electrolyte include polyacrylates, polyurethanes, polydialkylsiloxanes, polymethacrylates, polyphosphazenes, polyethers, and polycarbonates, and may be polymerized in situ in the presence of the electrolyte to trap the electrolyte therein as the polymerization occurs. Known polymers for pure polymer electrolyte systems include polyethylene oxide (PEO), polymethylene-polyethylene oxide (MPEO) or polyphosphazenes (PPE). Known lithium salts for this purpose include, for example, LiPF.sub.6, LiClO.sub.4, LiSCN, LiAlCl.sub.4, LiBF.sub.4, LiN(CF.sub.3 SO.sub.2).sub.2, LiCF.sub.3 SO.sub.3, LiC(SO.sub.2 CF.sub.3).sub.3, LiO.sub.3 SCF.sub.2 CF.sub.3, LiC.sub.6 F.sub.5 SO.sub.3, and LiO.sub.2 CF.sub.3, LiAsF.sub.6, and LiSbF.sub.6. Known organic solvents (i.e., vehicles) for the lithium salts include, for example, propylene carbonate, ethylene carbonate, dialkyl carbonates, cyclic ethers, cyclic esters, glymes, lactones, formates, esters, sulfones, nitriles, and oxazolidinones.
Lithium cells made from pure polymer electrolytes, or liquid electrolytes entrapped in a polymer matrix, are known in the art as "lithium-polymer" cells, and the electrolytes therefor are known as polymeric electrolytes. Lithium-polymer cells are often made by laminating thin films of the anode, cathode and electrolyte together wherein the electrolyte layer is sandwiched between the anode and cathode layers to form an individual cell, and a plurality of such cells are bundled together to form a higher energy/voltage battery. In making such cells, it is desirable that the thin films be flexible and robust so that they can be handled without damage.
While electrodes made from manganese oxide spinels are relatively inexpensive, and produce cells having a desirable high discharge terminal voltage (i.e., 4 volts), they are not without problems. For example, electrodes made therefrom have poor conductivity and require the addition of conductive fillers (e.g., carbon) to enhance conductivity. The addition of such fillers reduces the energy density of the electrode. Moreover, recharging cells requires impressing a voltage thereon which exceeds the discharge terminal voltage of the cell. Hence for cells having manganese oxide spinel cathodes, it takes at least 4.1 volts (and preferably more) to intercalate lithium from the electrode during charging of the cell. Above about 4.5 volts, however, the solvents for the electrolyte oxidize and decompose. Hence, it is necessary to carefully control the charging voltage of such cells below the decomposition potential of the solvent in order to prevent degradation thereof. Furthermore, due to the crystalline structure of spinel manganese oxide, their reversible capacity and cycle life are sensitive to overcharge and overdischarge. Discharge of manganese oxide spinel cells must be cut-off when the terminal voltage falls to about 3.4 volts. This limits the capacity of the material which typically peaks at about 140 mAh/g. Below about 3.4 volts, the spinel form of the manganese oxide undergoes structural transformation when additional lithium is inserted into LiMn.sub.2 O.sub.4 and it converts to the orthorhombic form which has very poor cycleability, and is very unstable causing the formation of other manganese oxides which are not electrochemically active. Still further, insertion of more than one lithium into spinel manganese oxide results in cation mixing between octahedral and tetrahedral sites which leads to continuous capacity decay. To avoid these problems, the cell voltage must be controlled electronically during the operation of the cell. Such control is very difficult to manage when a number of large lithium cells are coupled together in series. Finally, spinel-type manganese oxide electrodes typically have internal surface areas less than about 40 m.sup.2 /g, which limit their intercalation capacity and the rate at which they can be discharged and recharged.